This paper documents the research for and development of the unified wind turbulence model block for a Commercial Off-the-Shelf (COTS) software package that allows for a graphical hierarchical block diagram representation of entire vehicles including environment and control models. Recognized standards were used as a basis for the COTS wind turbulence block's operational requirements. Standards used were MIL-F-8785C and MIL-HDBK-1797, which provide guidelines for modeling wind turbulence. Additionally multiple papers on wind turbulence were referenced.

Creating a Unified Graphical Wind Turbulence Model from Multiple Specifications

In the first part, we present a method of numerical simulation of random gaussian fields, with values in a vector space, homogeneous and non homogeneous We give a thorough description with some addenda for the general case of vector valued random fields, including some properties which seem to us essential in order to control the quality of the numerical simulation The case of real gaussian processes, stationary and non stationary is of course a special case of the general results The second part of the paper is dealing with the numerical simulation of the atmospheric turbulence

Numerical methods and mathematical aspects for simulation of homogeneous and non homogeneous gaussian vector fields

In this paper a Constrained Finite Time Optimal Controller (CFTOC) for the problem of trajectory tracking of an Unmanned quadrotor Helicopter (UqH) is presented. The controller is designed based on a Piecewise modeling of the quadrotor for the rotational angles, that are inherently coupled to the translation equations of motion. The proposed CFTO-control scheme is able to take under certain factors that degrade the performance of the helicopter such as the physical and mechanical constraints of the system. Simulation studies illustrate the efficacy of the proposed scheme and also its ability to attenuate external disturbances that are introduced from environmental causes such as wind gusts.

Constrained-control of a quadrotor helicopter for trajectory tracking under wind-gust disturbances

In order to meet increasing demands on performance and reliability of Unmanned Aerial Vehicles, nonlinear and adaptive control techniques are often utilized. These techniques are actively being studied to handle nonlinear aerodynamic and kinematic effects, actuator saturations and rate limitations, modeling uncertainty, and time varying dynamics. This chapter presents an overview of some tools and techniques used for designing nonlinear flight controllers for UAVs. A brief overview of Lyapunov stability theory is provided. Nonlinear control techniques covered include gain scheduling, model predictive control, backstepping, dynamic inversion based control, model reference adaptive control, and model based fault tolerant control.

Nonlinear flight control techniques for unmanned aerial vehicles

The purpose of the spatial model considered in the present investigation is to generate the wind environment for use by others for flight simulation. Winds and gusts are provided over any finite area (e.g., aircraft body) from which aircraft loads and moments may be calculated. Three-dimensional autospectral information and correlation are contained in the data. It is pointed out that the three-dimensionality as contained in the spatial model affords much greater realism than widely used one-dimensional models. The resulting simulated wind is a nonlinear, non-Gaussian combination of real atmospheric winds and Gaussian, three-dimensional turbulence modulated by gust intensities which may vary freely as desired over space. The turbulence as represented by a product of a varying gust intensity and simulated turbulence is nonlinear and non-Gaussian.

A spatial model of wind shear and turbulence

An improved three-dimensional, nonrecursive model for atmospheric turbulence has been developed that provides for simulation of both instantaneous gusts and gust gradients along the flight path of the Space Shuttle. The one-dimensional gust and gust gradient spectral models, which form the basis for the simulation scheme, are developed from three-dimensional, von Karman spectra, integrated over finite limits based on the characteristic dimensions (length, width, and thickness) of the flight vehicle. By means of the simulation process, nondimensional time series for both gusts and gust gradients have been generated and stored on a series of magnetic tapes for four altitude bands ranging from 0 to 10,000 m. These Shuttle Simulation Turbulence Tapes (SSTT) have been validated by means of spectral and statistical analyses with very satisfactory results. The dimensionless form of the time series, coupled with the use of a von Karman spectral model (as opposed to a Dryden model), distinguish the SSTT from earlier turbulence simulation concepts.

Stephen R. Smith

Papers

Simulation of Atmospheric Turbulent Gusts and Gust Gradients